The development of gingivitis and periodontal disease in humans depends on the formation of dental plaque in close proximity to host tissue. Adherence of a limited number of gram-positive oral bacteria including Actinomyces viscosus and Streptococcus sanguis is thought to promote the adherence of a variety of gram-negative anaerobic organisms. Adherence of Actinomyces viscosus to the tooth surface depends on the presence of the cell surface fimbriae designated type 1 which are functionally and immunologically distinct from the type 2 fimbriae identified on the organism. A recent study has further demonstrated that the acidic proline rich proteins of salivary pellicle function as the receptors for the fimbriae mediated bacteria-tooth interaction. Whereas the functional properties of the fimbrial antigens of this organism are well defined, studies are needed to further characterize the structure of these fimbriae. The primary goals of the present proposal are to examine the molecular basis of the type 1 fimbriae mediated adherence of A. viscosus T14V to acidic proline rich protein-coated hydroxyapatite and to study the genetic organization of fimbrial and fimbrial-associated genes involved in synthesis and function of the fimbriae. The specific objectives of the proposal, therefore, are to: (1) generate monoclonal antibodies against the type 1 adhesin(s) of A. viscosus T14V; (2) use monoclonal antibodies against the adhesin to screen genomic clone banks of A. viscosus in E. coli for the expression of the adhesin; (3) isolate and characterize the adhesin gene; (4) isolate and characterize the type 1 adhesin from A. viscosus as well as from a cell lysate of E. coli clone containing the adhesin gene and evaluate the ability of the adhesin to promote bacterial adherence; (5) isolate chromosomal fragments encompassing the genes involved in fimbriae biogenesis and function; (6) develop a transformation system for Actinomyces and to begin studies on the functions of the fimbrial genes against an Actinomyces background. These studies should advance our understanding on the initial process of plaque development. Moreover, these experiments will provide the base for future long term studies focusing on genetic analysis of the fimbrial-associated genes and the control of gene expression.